The present invention relates to a cordless telephone for making wireless communications between a base unit and a handset unit, and controlling transmission power of handset unit, and method for controlling transmission power of handset unit in the cordless telephone.
Recently, along with wide spread of cordless telephones, the battery life of the handset unit of the cordless telephone is becoming an important issue. The base unit of the cordless telephone is connected to a commercial power source, and battery is not used.
The handset unit operates on its battery. Therefore, when the power consumption of the handset unit is large, the battery life is short. The battery needs to be replaced frequently, and the running cost increases, and possibility of disability of use increases.
To extend the battery life as long as possible, it has been proposed to control the transmission power in the handset unit (hereinafter called handset unit power). In this handset unit power control method, the handset unit power is controlled based on received signal strength indicator (RSSI) value of the handset unit.
The higher the RSSI value is, the shorter the distance between the base unit and handset unit is, and it seems there is no problem if the handset unit power is set at low transmission power (called xe2x80x9cLxe2x80x9d hereinafter; in the case of high transmission power, xe2x80x9cHxe2x80x9d). In this case, the handset unit power is set at xe2x80x9cLxe2x80x9d, and the power consumption of the battery is saved, and the battery life is extended.
Thus, based on the RSSI value, generally, the handset unit power is controlled, and the power consumption is saved.
It is hence an object of the invention to present a cordless telephone further easier to use while saving power consumption. More specifically, the invention presents a cordless telephone for controlling handset unit power while keeping the reception quality, in consideration of bit error rate (BER) as well as RSSI value, and a method of controlling the handset unit power.
The cordless telephone of the invention comprises:
a) a base unit controller incorporated in a base unit for outputting a control signal for controlling the handset unit power responsive to the CRC error rate (CRCE) and received signal strength indicator (RSSI) value of the base unit, and
b) a handset unit controller incorporated in a handset unit for receiving a control signal from the base unit and controlling the handset unit.
The base unit controller
i) requests the handset unit controller to set the handset unit transmission power (handset unit power) to high value when the CRCE is larger than a predetermined value,
ii) requests the handset unit controller to set the handset unit power to high value when the RSSI value is not more than a predetermined value, and
iii) requests the handset unit controller to set the handset unit power to low value when the CRCE is not more than a predetermined value and the RSSI value is larger than a predetermined value.
The handset unit controller sets the handset unit power base on at least one of the control signal and the determination by the handset unit controller.
The control method of handset unit transmission power in the cordless telephone of the invention comprises the steps of:
a) outputting a request for controlling the transmission power of a handset unit, responsive to the CRC error rate (CRCE) and received signal strength indicator (RSSI) value of the base unit, in the base unit, and
b) controlling the handset unit, by receiving a control signal, in the handset unit.
The base unit,
i) requests the handset unit controller to set the handset unit power to high value when the CRCE is larger than a predetermined value,
ii) requests the handset unit to set a hand set transmission power at high value when the RSSI value is not more than a predetermined value, and
iii) requests the handset unit power to set the handset unit power to low value when the CRCE is not more than a predetermined value and the RSSI value is larger than a predetermined value.
The handset unit sets the handset unit power based on either the control signal or the determination by the handset unit controller.
Thus, the control method of handset unit power for controlling the handset unit power based on both RSSI value and CRC error rate is obtained.